Numerous attempts have been made to provide voice communication within environments having a high ambient noise level. Particularly, it has been desirable to provide a system in high ambient noise conditions as found in aviation, competitive motor sports such as racing cars and boats, industrial plants, crowd noise, public safety and military operations.
Known voice transmission systems designed for high ambient noise conditions generally operate on the principle of audio vibration pickup of sound signals by bone and tissue conduction through the head of a person wearing an earpiece. U.S. Pat. No. 4,150,262 shows a typical voice transmission system having an earpiece formed to fit into the external auditory canal. The earpiece structure is hard and closely contacts the external auditory canal wall to enhance the capability of transmitting sound vibrations from the surrounding bone structure. A piezo element mounted inside the earpiece vibrates when the user utters voice sounds causing the bone structure to vibrate. In some embodiments, the air within the external auditory canal between the earpiece and the tympanic membrane is allowed to escape thereby reducing the effect of physically blocking the external auditory canal. No attempt is made to obtain voice sounds from the air within the auditory canal.
U.S. Pat. No. 4,588,867 discloses an ear microphone comprising a pickup piece having a vibration/electrical signal converter element. The pickup piece and a support body are composed of a rigid material having a large mass to enhance the pickup of sound vibrations through bone and tissue conduction. The large mass rigid member is combined with resilient material in an effort to reduce noise generated by external vibrations on the ear microphone. The principle of voice communication used in U.S. Pat. Nos. 4,150,262 and 4,588,867 depends upon audio vibration pickup via bone and tissue conduction. Therefore, it is virtually impossible for these prior art devices to be used under ambient conditions where the noise levels are greater than 90 decibels.
U.S. Pat. No. 2,938,083 shows an earpiece disposed at the opening of the external auditory canal while the speaker and amplifier system is located outside the earpiece member. The system delivers inbound sound through the earpiece to the tympanic membrane but does not handle outbound voice sounds. This system does not address use in a high ambient noise environment, and therefore is not designed for such use.
The in-ear hearing aid disclosed in U.S. Pat. No. 2,987,584 includes a canal extension section having a structural configuration for maintaining the earpiece in position without slipping or using exterior clamps for holding the unit to the ear. A plastic sound tube extends through the center of the canal extension section for delivering inbound voice sounds in accordance with standard hearing aid technology. No outbound voice transmission is possible with this known device under high ambient noise conditions.
Re. Pat. No. 26,174 discloses a hearing aid earpiece structure that fits the outer ear and a portion of the auditory canal. The earpiece has self-contained electronic control circuitry. An electro-formed metal housing has an auditory canal extension providing an effective seal to facilitate the inbound transmission of sound within the auditory canal both by air conduction and the audio vibration pickup of sound by bone conduction. Specific techniques are disclosed to enhance the degree of inbound sound transmission by bone conduction. A single flexible tube connects the inbound voice sound outlet of a speaker to an open end port disposed a space distance from the tympanic membrane of the earpiece user.
U.S. Pat. No. 2,535,063 discloses the typical commercially available two-way communication systems. Sound is sent and received through the external auditory canal to effect two-way communication. A transducer functions both as an earphone to direct inbound sound to the ear canal and as a microphone for transmitting outbound voice sounds from the ear canal to a remote location. It has been found that such commercially available systems are not capable of operating under ambient conditions with noise levels greater than 90 decibels. That is, two-way communication of a clear intelligible voice sound signal under ambient conditions with noise levels in excess of 90 decibels is not possible. With such high ambient noise conditions, the externally disposed transducer will necessarily modulate creating noise interference thereby causing the voice sound signal to become unintelligible.
U.S. Pat. No. 3,819,860 discloses an ear-borne transceiver using two audio passageways that are continuously open at all times and include a filter mechanism for eliminating background noise. This known ear-borne transceiver and circuit system enables a person to simultaneously transmit and receive through the passageways which are continuously coupled in open communication to the ear of the wearer of the device. Thus, substantially normal conversation can be effected so that the user can transmit while listening to himself by way of the receiver. This system is distinguished from the U.S. Pat. No. 2,535,063 which employs two channels which are mutually exclusive whereby the operator must either transmit or receive but cannot hear himself speak when transmitting. The structure of U.S. Pat. No. 3,819,860 is unworkable in a high ambient noise situation because of the obvious feedback problems existing where both channels are continuously open as disclosed.
U.S. Pat. No. 2,946,862 discloses an ear protector and communication equipment designed to effect sound attenuation while employing a two-way communication system incorporating a microphone and receiver located in an "earmuff" type of ear protector shell. This system is particularly designed to avoid the use of an earpiece having a structural configuration for insertion in the user's ear.
Noise free voice transmission through the external auditory canal under high ambient noise conditions at noise levels greater than about 90 decibels has heretofore been unattainable. The noise levels within the higher decibel range are known to have an exponential character. For example, at 100 decibels there is a certain noise level. At 103 decibels the noise level is about twice as great as at 100 decibels. At 106 decibels the sound pressure level is again twice that found at 103 decibels and so forth. At ambient noise levels of about 125-130 decibels, clear voice transmission through the auditory canal is new and unexpected.
The best boom microphone system using a mike located in front of the mouth is incapable of performing at a noise level or sound pressure much over about 110 decibels. Under these conditions, the boom mike will be substantially resting directly on the lips. Consequently, under such conditions as found in competitive motor sport events, the boom mike simply gets in the way because of the activity in the driver's cockpit.
With respect to the patent disclosures discussed above, at the noise levels of greater than about 90 decibels and up to about 140 decibels, the bone and tissue of the earpiece wearer would transmit external noise significant enough to render these prior art devices incapable of clear voice transmission.